In general, a mobile communication system operates in a licensed band in order to assure QoS of a user. In recent years, a 3GPP standard organization has started a discussion about the use of an unlicensed band (alternatively, spectrum) of a long term evolution (LTE) system.
A 2.4 GHz or 5 GHz band in the unlicensed band is dominantly used by a WiFi system. When the LTE system uses the unlicensed band, a resource allocation method and an interference avoidance function for the coexistence with the WiFi system should be considered. In the case of WiFi, a carrier sense multiple access (CSMA)/collision avoid (CA) method is used in order to access a radio resource. On the contrary, since a general LTE system gets a license (approval) for the band in advance, the general LTE system operates based on scheduling.
Under such an environment, in order for the wireless communication or mobile communication system using the licensed band, such as the LTE system to use the unlicensed band, a coexistence protocol that may be operated to coexist with a system that operates in the unlicensed band, such as the WiFi system, or the like is required.